Now, CNN finds that Rubio has broken into double-figure support among Republicans nationally. He’s at 11 percent, according to CNN, basically tied with Scott Walker, Rand Paul, and Mike Huckabee. Only Bush does appreciably better 17 percent, not a hugely impressive number given his name.

Moreover, among self-identified Tea Party Republicans, Rubio has 14 percent support. This is just one point behind Walker and Ted Cruz, who share the lead with this cohort.

But the question of immigration reform lurks for Rubio. Mickey Kaus notes that on Sunday, Bob Schieffer asked the Florida Senator whether as president he’d sign his own “Gang of 8″ immigration bill. Rubio ducked, telling Schieffer that the question is “a hypothetical.”

Kaus speculates that Rubio declined to declare he wouldn’t sign the legislation because he doesn’t want to alienate potential big-money supporters like Sheldon Adelson and Paul Singer. It’s certainly possible that this consideration has entered Rubio’s thinking. But there are other reasons for Rubio not to state categorically that he wouldn’t sign the Schumer-Rubio legislation.

Rubio didn’t just sponsor this bill, he devoted months to pushing for passage, arguing in its favor to anyone who would listen. For Rubio now to say he wouldn’t sign his own legislation would raise as many questions as it would put to bed.

Foremost among the questions would be this one: Why should America elect as its president a man erratic enough to pour his heart into enacting legislation that, if presented to him now on a silver platter, he would veto?

It would be one thing for Rubio to say that he wouldn’t now push for Schumer-Rubio because it would be a distraction from more urgent priorities, or whatever. It would be quite another to confess to having been nisguided just two years ago as to push for legislation he would now refuse to sign.

There is also Rubio’s need to appeal to Hispanic voters in the general election. Kaus dismisses this concern, saying that if Rubio gets the nomination “there will be plenty of ways to backslide and re-suck-up to Latino ethnocentrists.”

I doubt that Rubio is this sanguine, and he’s right not to be. Rubio has flip-flopped on this issue too often to assume that he can comfortably “backslide” again.

It will be hard for Rubio to get away indefinitely with dodging Schieffer’s question on the grounds that it is hypothetical. But he’s wise to keep his options for answering open for as long as he can.